1. Field of the Invention
The present invention relates to techniques for storage or handling of electronic parts and, more particularly, to a carrier used for carrying and storing surface-mount type electronic parts, such as surface-mount packages.
2. Description of the Related Art
Conventionally, for surface-mount electronic parts such as surface-mount IC or LSI packages, an electronic part provided with a molded body and a plurality of leads extending from the body is usually carried and stored in such a condition as to be accommodated in an exclusive container or carrier, to eliminate dust accumulation, lead damage, short circuits, and so on. The known structure of the carrier is, e.g., a tray (FIG. 1) or a carrier tape (FIG. 2).
As shown in FIG. 1, the conventional tray 1 includes a plurality of storage sections 3 defining recesses for individually receiving electronic parts (not shown) in a regular arrangement as, e.g., a matrix. A manufacturer of electronic parts ships the tray 1 with the electronic parts being accommodated in the storage sections 3. Then, a user of electronic parts takes out the electronic parts from the respective storage sections 3 of the tray 1 by using, e.g., an automatic mounting machine, and mounts them on circuit boards.
On the other hand, as shown in FIG. 2, the conventional carrier tape 2 includes a plurality of storage sections 5 defining recesses for individually receiving electronic parts (not shown) in a regular arrangement along a longitudinal line. The adjacent storage sections 5 are connected through a connecting section 6 with each other, and a number of sprocket holes 7 are provided along one side edge of the tape to penetrate through a tape portion near the storage sections 5. A manufacturer of electronic parts usually ships the carrier tape 2 rolled on a reel 9 with the electronic parts being accommodated in the storage sections 5 and with a cover film 8 being attached to the tape to cover all the storage sections 5. Then, a user of electronic parts unrolls the carrier tape 2 from the reel 9 by using an automatic mounting machine, peels or removes the cover film 8, sequentially takes out the electronic parts from the respective storage sections 3 while the tape 2 being progressively fed, and mounts the electronic parts on circuit boards. This constitution has an advantage in that the time required for an automatic mounting process can be significantly shortened in comparison with the above-mentioned tray in which the electronic parts are distributed on one plane and are taken out one by one for a mounting operation.
In the above-described conventional carriers for electronic parts, a problem has been arisen in which the electronic parts are moved in the corresponding storage sections during carrying and storing, which results in a lead damage and/or a difficulty in smoothly taking out the electronic parts by the automatic mounting machine. To solve this problem, the solution has been provided wherein a support section is formed inside each storage section of the carrier for securely supporting the electronic part in a predetermined position therein.
For example, the publication of Japanese Patent No. 2599010 discloses a carrier tape which is provided on the bottom walls of storage sections with projections for supporting electronic parts. The projections of each storage section are formed as four ribs arranged along four sides of a rectangular profile in a plan view on the bottom wall. Each rib is provided with a support surface for supporting the molded body of the electronic part, and a ridge uprightly extending from the outer edge of the support surface. The molded body of the electronic part accommodated in the storage section is held between the support surfaces of the ribs and the cover film, and is secured in a lateral direction between the ridges of the opposed ribs. Another carrier tape having a similar structure is also disclosed in Japanese Examined Patent Publication (Kokoku) No. 7-23172.
In the above-described conventional carriers for electronic parts, the storage sections are generally formed as recesses, in a plastic sheet material having a uniform thickness, through a vacuum forming process or a compression molding process. Accordingly, the relatively thinner plastic sheet material may result in the reduced thickness of the walls of the storage sections formed as recesses and thus in an insufficient mechanical strength thereof. Particularly, in the case of carrier tape, if the storage sections of the carrier tape have the thinner walls and lack in the mechanical strength of the walls, the walls, or especially the bottom walls, of the storage sections may be compressed and deformed by the underlying portion, or especially the bent connecting section, of the carrier tape rolled on a reel. The deformation of the walls of the storage sections may cause the accommodated electronic parts, or particularly the leads thereof, to be damaged.
The problem of the insufficient mechanical strength of the walls of the storage sections may become significant when the dimension of the electronic part to be accommodated is increased. In the case of forming the storage sections by a vacuum forming or a compression molding process, if the dimensions of the storage sections are enlarged so as to correspond to the dimension of the electronic parts, the rate of reduction of the thickness of the storage section walls relative to the thickness of the plastic sheet material rises. However, it is not desirable to merely increase the thickness of the plastic sheet material in order to thicken the storage section walls, because the entire stiffness of the molded carrier tape would be unnecessarily enhanced and thereby the operability for rolling the carrier tape onto the reel would be deteriorated. Therefore, for the electric part having relatively large dimension with, e.g., every side being 2 to 3 cm or more, the tray has been conventionally used, instead of the carrier tape, regardless of the reduction of an automatic mounting speed.
Also, the carrier for electronic parts is normally made as a disposable member because of the requirement of avoiding dust accumulation, and is disposed of in the form of small pieces cut by, e.g., a cutter after using the carrier or after removing the electronic parts. Accordingly, if the thickness of the plastic sheet material is merely increased in order to improve the strength of the storage section walls, the entire stiffness of the carrier would be unnecessarily enhanced, which causes a disadvantage that the cutter is worn away in a cutting process in a relatively short time. This may be caused in the case of the tray and of the carrier tape.
The applicant of the present application has proposed, in a specification of copending earlier Japanese patent application No. 9-83769 (filed on Apr. 2, 1997), a method of manufacturing a carrier tape wherein an injection molding process is adopted instead of the vacuum forming or compression molding process. The injection molding process enables the thicker walls of storage sections and the thinner connecting sections to be simultaneously integrally molded, so that the mechanical strength of the storage section walls can be improved without unnecessarily enhancing the entire stiffness of the carrier tape. However, in this solution, first a plurality of carrier pieces, each of which includes at least one storage section, are formed through the injection molding process, and then the molded carrier pieces are connected together into a tape-form to produce the carrier tape. Consequently, it is required to prevent connecting areas between the adjacent carrier pieces from being broken due to an external force such as bending or stretching force applied thereto upon rolling the carrier tape onto a reel or upon unrolling the carrier tape from the reel by an automatic mounting machine.